Seismic Stratigraphy of Carbonate Depositional Sequences, Upper Jurassic-Lower Cretaceous, Neuquén Basin, Argentina
Robert M. Mitchum, Jr., Miguel A. Uliana, 1985. "Seismic Stratigraphy of Carbonate Depositional Sequences, Upper Jurassic-Lower Cretaceous, Neuquén Basin, Argentina", Seismic Stratigraphy II: An Integrated Approach to Hydrocarbon Exploration, Orville Roger Berg, Donald G. Woolverton
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The Upper Jurassic-Lower Cretaceous interval in the Neuquen basin, Argentina, provides a good example of carbonate sedimentary response to eustatic sea-level change in a rifted basin that has produced hydrocarbons for over 50 years. We analyzed the area using an integrated stratigraphic approach, including seismic stratigraphy for sequence id en tification and configuration, wells and outcrops for lithologies and porosity types, and outcrops for paleontological age, ecological data, and detailed physical stratigraphy. Our study shows that the Vaca Muerta, Quintuco, Loma Montosa, and Mulichincoformations are time-transgressive lithofacies units within a series of prograding sequences that laterally filled the shallow, stable basin. There are at least nine clinoform-shaped depositional sequences, and they span the Tithonian, Berriasian, and Valanginian stages. All of them consist of seismically mappable shelf, shelf-margin, slope, and basin facies. In the wells tied to seismic data, the predominantly carbonate reservoir rocks of the Loma Montosa and Quintucoformations represent, respectively, the inner- and outer-shelf segments of individual clinoform sequences. Hydrocarbon-source shales of the Vaca Muerta Formation occur in slope and basin positions. The youngest prograding unit is characterized by shelfal to continental sandstones of the Mulichincoformation. The degree of shelfward restriction, lateral progradation, and vertical aggradation of the sequences appears to be strongly controlled by global trends of eustatic rises and falls. Other depositional controls, such as thermal subsidence and sediment influx, occur at slow, nearly constant rates in medial to late stages of basin evolution.
An idealized shelf-to-basin lithologic model of a given sequence progresses from terrestrial sandstones and shales through marine inner-shelf micritic limestones, dolomites, and shales; middle-shelf oolitic and skeletal carbonates and shales; outer-shelf molluscan-micritic limestones and shales; and slope and basin dark organic shales.
Outcrops along the western basin margin exhibit depositional characteristics similar to those of the subsurface. In the western outcrop area, lithostratigraphic units are time-transgressive from south to north toward the basin center. In the northwestern outcrop area (Malargtie), the timing and depositional response to eustatic changes can be documented through interpretation of detailed stratigraphic and paleontologic observations by other authors.